A solid rocket motor or composite propellant rocket motor is a rocket with a motor that uses solid propellants comprising a fuel and an oxidizer. The solid propellant is normally in the form of a propellant grain placed within the interior of the rocket motor (e.g. in the combustion chamber) and burned to produce hot gases which, in turn, exit through the throat and nozzle of the rocket motor at high velocity to provide thrust which propels the rocket in the opposite direction.
Although liquid rockets are commonly used today due to better efficiency and controllability as compared to solid rockets, solid rockets are still used in certain applications primarily because they are relatively easy to manufacture and generally exhibit excellent performance characteristics. In addition, solid rockets are generally less complex as compared to those employing liquid fuels. However, unlike liquid propellant rockets, solid propellant rockets are unable to control or alter their thrust characteristics after ignition by adjusting the amount of fuel entering the area of combustion.
Known composite propellant rocket motors have generally been shut-off by a process of sudden depressurization, but the Present Inventors are not aware of a disclosed shut-off process functional at operational pressures. Some shut-off processes involve a destructive means of operation, such as requiring physical rupture of the case in some fashion to depressurize the combustion chamber. This practice has several pitfalls, such as severe structural damage to the motor and uncontrolled burn-off of the remaining solid propellant.
In one application for solid rockets, the interception of attacking ballistic missiles above the atmosphere is achieved by launching an interceptor missile against the attacking missile. The interceptor is directed toward the attacking missile (the so called “target”) and preferably hits it or explodes in the vicinity of the target, generally causing the target severe damage and perhaps even complete destruction. Typically, the interceptor comprises a one (or several) stage booster and the so-called “kill vehicle”.
Generally, the kill vehicle is required to maneuver in space in order to adjust its position with regard to its target, to compensate for cuing errors raised by ground or space detection and tracking systems and onboard navigation errors and in response to tracked target maneuvers. Future missile defense systems will generally employ kinetic-energy kill vehicles. The two primary components of a kinetic-energy kill vehicle include sensors for target identification and tracking, and a divert and attitude control system (DACS) for maneuvering the kill vehicle. One of the promising technologies for the interceptor's DACS propulsion is the use of a solid rocket motor. A solid DACS is preferable over a liquid-based system for reasons described above.
To satisfy the extreme requirements of a DACS motor, which can include trajectory adjustment and multiple firings, the solid rocket motor must be able to be extinguished and relit, generally a plurality of times. To date, the extinguishment of burning solid propellants does not occur naturally, so the available technology generally requires a complicated rapid depressurization technique to stop the propellant's burning.